First Principles Studies of Interface Dielectric Properties of Polymer/metal-oxide Nanocomposites}

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dc.contributor.advisor Wenchang Lu, Committee Member en_US
dc.contributor.advisor Zhilin Li, Committee Member en_US
dc.contributor.advisor Marco Buongiorno Nardelli, Committee Member en_US
dc.contributor.advisor Jerry Bernholc, Committee Chair en_US Yu, Liping en_US 2010-04-02T19:09:37Z 2010-04-02T19:09:37Z 2009-07-29 en_US
dc.identifier.other etd-07272009-164521 en_US
dc.description.abstract This thesis is devoted to studying interface dielectric properties of polymer nanocomposites from first principles. We aim to understand at atomic scale the role of interface effects and the dielectric finite size effects of nanoparticles in determining the effective dielectric properties of polymer nanocomposites. To study surface effects from first principles, we first investigate the two common methods, namely dipole correction and Coulomb cutoff, used to eliminate the artificial effects introduced by using the supercell approximation. We implement Coulomb cutoff technique in a plane-wave-based density functional theory code and compare it with dipole correction for the same system under the same conditions. By comparison, both methods are shown to be equivalent and able to remove the artificial effects of periodic images very accurately. We also find that a combination of these two methods offers an easy way to distinguish the localized bound states of interest from highly delocalized unoccupied states while using a relatively small supercell, and to ascertain the convergence of the results with respect to supercell size. To understand the dielectric properties at the atomic scale, we develop a new nanoscale averaging model to connect the macroscopic quantities to the corresponding microscopic ones. This model allows us to compute the spatially resolved local dielectric permittivity, including the critically important ionic contributions, for interfaces and other complex structures. In this model, a simple way of evaluating real-space decay length of the nonlocal dielectric functions is also proposed. By using the dipole correction and our averaging model in supercells, we calculate the optical and static local dielectric permittivity profiles for polymer (polypropylene) / metal-oxide (PbTiO$_3$ and alumina) nanocomposites. Our {em ab-initio} results show that metal-oxide/polymer interface effects are very localized and are mostly confined to the metal-oxide surface side, and that nanoscale metal-oxide slabs can on average retain the macroscopic value of bulk dielectric permittivity. These findings suggest that classical mixing laws associated with macroscopic composites can be applied to model the overall dielectric constant of a real polymer/metal-oxide nanocomposite system. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dis sertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject Coulomb cutoff en_US
dc.subject dipole correction en_US
dc.subject interface en_US
dc.subject DFT en_US
dc.subject nanocomposite en_US
dc.subject polymer en_US
dc.subject ferroelectric en_US
dc.subject alumina en_US
dc.subject PbTiO3 en_US
dc.subject polypropylene en_US
dc.subject dielectric permittivity en_US
dc.title First Principles Studies of Interface Dielectric Properties of Polymer/metal-oxide Nanocomposites} en_US PhD en_US dissertation en_US Physics en_US

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